1. Field of the Invention
The present invention relates to network devices and, more particularly, to a network device having a multiple component connector plane configured to interconnect functional cards.
2. Description of the Related Art
Data communication networks may include various nodes, routers, switches, hubs, and other network devices coupled to and configured to pass data to one another. Nodes, routers, switches, hubs, and other network devices will be referred to herein as “network devices.” Data is communicated through the data communication network by passing data packets (or segments or data cells) between the network devices by utilizing one or more communication links between the devices. A particular data packet may be handled by multiple network devices and cross multiple communication links as it travels between its source and its destination. Network devices are typically configured to transport data elements from one interface to another to facilitate delivery of packets over a network. Network devices are not configured to process the data and/or alter the data within the packet, except as necessary to make any required transportation decisions or perform functions related to packet transportation.
Conventional network devices include a plurality of input/output cards (I/O cards) configured to receive and output data, and a plurality of processor cards configured to process information and instruct the I/O cards how to receive and output the data. A printed circuit board forming a back plane or mid-plane is used to interconnect the I/O cards and processor cards.
As data networks have grown in complexity and speed, the network devices used in those networks have likewise increased in complexity and speed. This complexity may be manifest in many ways, including in the back-plane or mid-plane used in the network device.
Points on a printed circuit board are interconnected by traces. If traces are required to cross over each other, multiple layers of traces vertically joined by vias must be used to form the required interconnections. As the printed circuit boards forming the mid-plane or back-plane become more complex, the number of layers has concomitantly increased. This complexity results in the mid-plane or back-plane having an increasingly large number of layers.
In printed circuit board manufacturing, the greater the number of layers required to be formed on a given printed circuit board the lower the yield during manufacturing, and hence, the greater the cost of the finished product. The cost per layer is typically is not a linear function, however, because the yield associated with manufacturing a high layer count printed circuit board is often significantly lower than the yield associated with manufacturing a lower layer count printed circuit board. Hence, printed circuit boards required for network devices have grown increasingly expensive.
Additionally, there are other limitations in the printed circuit board manufacturing process that circumscribe the number of layers that can be cost effectively manufactured. One such limiting factor is the aspect ratio of the thickness of the printed circuit board to the connector hole diameter. Specifically, given a set aspect ratio, the maximum thickness of the printed circuit board will be defined by the diameter of the pins being used to connect the I/O cards and processor cards to the printed circuit board. The number of layers achievable on the printed circuit board, given the defined board thickness, may then be determined based on the material substrate technology to achieve the design layer-to-layer impedance requirements. However, as the number of interconnections between the I/O cards or processor cards, and connector plane have increased, the individual connector pins have decreased in both pitch and pin diameter, resulting in a reduced available board thickness.